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31.
32.
Per Geijer 《International Journal of Earth Sciences》1935,26(5):351-366
Zusammenfassung Seit einem früheren Stadium der geologischen Erforschung der nordschwedischen Eisenerzlagerstätten vom Typus Kiruna — meistens apatitreiche Magnetiterze — war es den damit beschäftigten Forschern klar, daß die Substanz der Erze im magmatischen Stadium von dem Magma der begleitenden Porphyrgesteine abgespaltet wurde. Die Natur und die Ursachen dieses Abspaltens müssen nach dem geologischen Befund beurteilt werden, denn es handelt sich um spätmagmatische Ereignisse in einem experimentell noch nicht erforschbaren Gebiet. Mineralparagenese, Struktur, Kontaktverhältnisse usw. deuten auf Kristallisation aus einem an leichtflüchtigen Gemengteilen reichen Magma (pneumotektische Gebilde). Der spätmagmatische oder restmagmatische Charakter der Erzbildung wird auch durch Übergänge nach Erztypen, die bei niedrigeren Temperaturen gebildet sind, klargelegt. Die Trennung zwischen Erz und Gestein erscheint ebenso scharf wie in den Fällen, in denen erzbildende Lösungen gasförmig abgeschieden worden sind. Die Abscheidung muß auch bei den hier behandelten spätmagmatischen Erzen auf die Wirkung der leichtflüchtigen Gemengteile (Magmagase) zurückgeführt werden. Genetisch verwandt sind sulfidische Erze, deren Anknüpfung an den Kirunatypus aus ihrem Apatit- und Magnetitgehalt hervorgeht, und die sich entweder aus pneumotektischen Magmen oder aus gasförmigen Lösungen kristallisierten. Mehr entfernt von der magmatischen Kristallisation folgen gewisse metasomatische Erze ähnlicher Zusammensetzung. Eigentümlicherweise zeigen aber die kontaktmetasomatischen Eisenerze in Kalkstein eine wesentlich andere Zusammensetzung der aus dem Magma stammenden Gemengteile, obgleich auch ihr Material aus dem Magma in Gasform entwich. Besonders auffallend ist der hohe Kieselsäuregehalt und die Seltenheit des Apatits. Diese Eigenschaften findet man auch in den Lagerstätten von diesem Typus, die in demselben Gebiet wie die Kiruna-Erze auftreten, und die mit den dortigen Tiefengesteinen verbunden sind. 相似文献
33.
34.
Per?WestmanEmail author Johanna?Borgendahl Thomas?S.?Bianchi Nianhong?Chen 《Estuaries and Coasts》2003,26(3):680-689
This study corroborates the hypothesis that nitrogen-fixing cyanobacteria have probably occurred as an important component
of the phytoplankton community in the Baltic Sea at least since brackish water conditions were initiated 8,50014C yr BP. Pigment analyses indicate that extensive occurrences started prior to a sharp increase in nutrient levels dated to
7,10014C yr BP. The cyanobacteria could have functioned as a natural trigger for eutrophication in the Baltic Sea by importing nitrogen.
This is also verified by a contemporaneous drop in the δ15N values from 4‰ to around 2‰. We further conclude that the spreading of cyanobacteria was probably caused by a decrease in
nitrogen∶phosphorus (N∶P) in the water mass that resulted from the intrusion of oceanic water with high P levels. The fractionation
of P in sediments indicated that iron-bound P was efficiently sequestered under anoxic conditions that occurred as a consequence
of the establishment of a stable stratification caused by the marine intrusion. This pool only showed minor variations around
3 μmol g−1 at the freshwater-brackish water transition. All P pools except the CaCO3 fraction showed a distinct increase around 9,30014C yr BP prior to the transition. We interpreted this increase as a change in preservation of organic matter or in the source
of the sediment. Slightly after 4,00014C yr BP there was a dramatic drop in all P pools without any corresponding decreases in total N and carbon. Total P decreased
from around 75 to 25–30 μmol g−1. The most dramatic drop occurred in the organic bound and the detrital apatite fractions, which decreased by a factor of
3–4. We explain this as a preferential regeneration of P, especially organic P, compared to other nutrients due to more prevalent
anoxic conditions. 相似文献
35.
36.
In the solvent extraction of metals, the distribution of the metal is usually dependent on the concentrations of several different species in the two phases. Despite this fact, distribution isotherms are usually presented as plots of Co as a function of Caq and these are used for a McCabe-Thiele type evaluation of a number of stages and flow rates, etc., each individual isotherm being valid only for one set of initial conditions; this treatment limits the possibilities of optimizing the system. In the present paper an extension of three-dimensional plots is suggested with special reference to the Cu/LIX64N extraction system. The distribution surface is defined and the general properties of the plots are outlined.A procedure is outlined whereby the surface can be represented on a two dimensional plot and a theoretical model for the surface can be superimposed.The paper also shows how distribution ratios (D values) are related to the surface. 相似文献
37.
38.
We have studied small-scale, filamentary features in 14 planetary nebulae and found that some structures are recurrent and
shaped like the letters V and Y, with the apex or stem pointing toward the central parts of the nebula. Two such filaments
containing dust, one in NGC 3132 and one in NGC 7293, were investigated in more detail. The mass and density of the filaments
were obtained from extinction measurements, and their physical properties were derived. We propose that the structures are
confined by magnetic fields, and derive magnetic field strengths of about 10−8 T, in line with earlier estimates. We also estimate the magnitude of the electric currents that we expect are generated in
these dynamic systems. We propose a theory where the magnetic fields control the sculpting and evolution of small-scale filaments.
This theory demonstrates how the substructures may form magnetized flux ropes that are twisted around each other, in the shape
of double helices. Similar structures, and with similar origin, are found in many other astrophysical environments. 相似文献
39.
40.
Lars Olov Andersson 《Physics and Chemistry of Minerals》2010,37(7):435-451
A number of different impurities are located in the open channels of natural beryl crystals. The rare Maxixe beryl contains
an unusual amount of NO2. The isoelectronic CO2
− radical is found in the irradiated Maxixe-type beryl. The NO2 radicals are distributed in the Be–Al plane of the crystal, with the nitrogen atom close to the oxygens of the beryl cavity
wall. These oxygens repel the negative CO2
− radical, which is located at the center of the beryl cavity and rotates around its O–O axis, which is parallel to the crystal
c-axis. When there is a nearby alkali ion at the center of the beryl channel, it reorients the CO2
− radical so that its bisector is parallel to the c-axis and points toward the positive ion. Different signals are analyzed for Li+, Na+, and another counter-ion, which probably is Cs+. The related NO3 and CO3
− radicals are the color centers in the investigated deep blue beryls. The slow decay of the color, which makes these beryls
useless as gem stones, is related to the decay of the hydrogen atoms which are present in these crystals. Evidence is given
that NO3 is created in Maxixe beryl by a natural process, while CO3
− in Maxixe-type beryl has been created by irradiation. The temperature dependence of the EPR signals of these two radicals
was investigated, but a definitive proof that they rotate at the center of the beryl cavity could not be given. EPR signals
from some other radicals in beryl have been observed and described. 相似文献